Why Rattlesnakes Are Bold Road Crossers

Why did the snake cross the road?

Maybe to swallow that proverbial chicken that wanted to see what was on the other side. Or maybe it didn't want to cross the road at all, because it had no stomach for what it might encounter along the way.

That may all sound a bit trivial, but it's serious science to Kimberly Andrews, a master's candidate in conservation ecology at the University of Georgia. Andrews and her faculty adviser, ecology professor Whitfield Gibbons, are up to their fangs in snakes these days, trying to answer questions that, frankly, not a lot of people have asked.

The research involves releasing all sorts of snakes along a section of roadway near the university's Savannah River Ecology Laboratory to see how, why and even if they are willing to try their luck at crossing about 15 feet of concrete. Andrews set up the two-year experiment, she says, because not a whole lot is known about why snakes are willing to cross a road.

What is known is that a lot of them don't make it.

"About a million vertebrates a day die on American roadways," she says.

Fragmented Terrain

No one knows exactly how many of those are snakes, because snakes in the wild are so secretive that it's hard to keep records on road kills, but Gibbons, a leading herpetologist, says it's a lot. Of course, you've got to have a lot of snakes to have a lot of road kills, so the figures vary greatly from one area to the next.

"I have personally seen as many as 20 dead snakes along a 10-mile stretch of road," says Gibbons, who spends a lot of time looking for snakes. "During a 30-year study in Florida, about seven snakes per day were found dead on a stretch of less than 20 miles of highway."

So given those odds, why would any snake want to venture across the road?

That's among the questions Andrews is trying to answer. Gibbons hints at one reason, even though the project is only half completed.

Most road kills among reptiles, he says, occur during mating season.

But Andrews' preliminary findings indicate that some snakes, regardless of their sexual prowess, just don't want to cross that road. And that's a problem.

A lot of ecological research these days is centered on something called "habitat fragmentation." Even if we succeed in preserving large chunks of land for wildlife, scientists are finding that if the chunks are separated, even by a narrow strip of roadway, that fragmentation can have a devastating impact on wildlife. Everything from finding a mate to avoiding predators to simply getting enough to eat can be adversely affected by fragmentation, because it reduces the range for animals that won't, or can't, venture across a barrier to happier hunting grounds.

Even birds are affected. Researchers have found, for example, that feathers grow more slowly for some bird species in fragmented habitats in the Amazon forest. That suggests they are stressed, and less likely to reproduce or even survive.

Other researchers have found that a fragmented habitat is more vulnerable to fire, because the animals may have nowhere to flee, and it is more susceptible to pollution.

And fragmentation can lead to genetic isolation, leading ultimately to offspring that are less capable of combating disease, according to various researchers.

Rattlers: Bravest Road-Crossers

So the seemingly simple question of why a snake crosses the road is not trivial at all. A snake that won't cross a narrow ribbon of concrete may have less of a chance to reproduce and survive than one that is willing to make a mad dash. And Andrews is finding plenty of snakes that won't go near the concrete.

For her research, Andrews uses snakes that have been captured in the sprawling wilderness that surrounds the lab. The area is rich with many species of snakes, some of which can be deadly, so she goes about her task with due caution.

The snakes are taken to the section of road, which is closed to vehicles, and slipped from a bag to beneath an inverted black plastic pot like those used by gardeners. The pot is hooked to a pulley atop a long stick. Andrews then retreats to the nearby woods and waits for the snake to settle down.

At this point, the snake has not seen the area, and when she yanks on a rope the pot is suddenly lifted. The snake can't see her, so as far as the snake is concerned, it's all alone in the woods, near a stretch of road.

With pencil in hand, Andrews records the actions of the snakes, some of which simply dart across the road. One common southern species, called a racer, can make it across the road in about 30 seconds, she says.

"You have a lot of snakes that will venture out onto the road, and they're kinda like, 'Whoa, I don't want any of this,' and they will turn around and exit," she says.

And some others, she adds, won't go near the road. Instead they beat a hasty retreat toward the woods.

The behavior varies greatly among species, she says. Rattlesnakes, for instance, don't seem to mind crossing the road and they take their sweet time about it. Maybe, she suggests, that's because a rattler has the ability to protect itself from predators and feels less vulnerable.

The racer doesn't seem to have any problems with the road, but Andrews is also studying snakes she encounters in the wild, and she has noticed a different behavior if the snake senses the presence of a vehicle.

"It freezes in the face of an oncoming car," she says, and that leads to an increase in road kills.

Rattlers may feel more secure as they meander across the roadway, but they rank among the leaders in road kills. One might suspect, given the rattler's nasty image, that many of those kills are not accidental.

Andrews sounds like she's having far too much fun with the project, given the fact that she has been fascinated with snakes all her life, but Gibbons thinks she's onto something.

"I think the research can be very significant in getting to the basic questions that have not been asked by herpetologists about why a snake, or any other animal, crosses a road in the first place."

Apparently it's a lot more complicated than just wanting to see what's on the other side.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.